Pro-regime demonstrators today tried to attack the US ambassador to Syria, an opposition leader said, as Damascus accused Washington of inciting "armed groups" into violence against its army.

Pro-regime demonstrators on Thursday tried to attack the US ambassador to Syria, an opposition leader said, as Damascus accused Washington of inciting "armed groups" into violence against its army.

The angry mob of nearly 100 Syrians tried to storm an office in the capital where the American ambassador, Robert Ford, had just arrived to meet opposition figure Hassan Abdelazim, the latter said.

"They were protesting in the street and at the entrance to the building. They tried to break down the door of my office, but didn't succeed," Abdelazim told AFP.

"As soon as the ambassador came in at around 11:00am (0800 GMT), we heard a noise outside and hostile slogans being chanted. The demonstrators tried to attack the office," he added.

Ambassador Ford was holed up inside the office for two hours before security forces arrived and he could return safely to the US embassy, said Abdelazim.

The US embassy confirmed his return in a brief statement to AFP, saying: "He is back and he is fine."

The incident came as the regime of embattled President Bashar al-Assad accused the United States of inciting "armed groups" into acts of violence targeting its military.

"Comments by American officials, notably (US state department spokesman) Mark Toner, are striking proof that the United States encourages armed groups to commit violence against the Syrian Arab army," a ministry statement said.

"The words of the state department spokesman, describing these terrorist acts as natural, are irresponsible and likely to encourage acts of terrorism and chaos in order to serve foreign goals against the interests of Syrians.

"Syria condemns strongly the US statements and affirms its determination to preserve its security and stability, to defend its citizens and to oppose all attempts to interfere in its internal affairs," said the statement.

Answering a reporter's question in Washington on Monday, Toner it came as no surprise that some arms are being sent to Syria's opposition.

"Well, look, I think it's not surprising, given the level of violence over the past months, that we're now seeing members of the military -- or, rather, members of the opposition -- begin to turn violent, or, rather, begin to use violence against the military as an act of self-preservation," Toner said.

"I would say that the opposition's shown extraordinary restraint in the face of the regime's brutality and demanding their rights through peaceful unarmed demonstrations," he added.

"It goes without saying that the longer the regime continues to repress, kill, and jail these peaceful activists, the more likely that this peaceful movement's going to become violent."

Angry mobs had stormed the American and French embassies in Damascus on July 11 after the two envoys visited the central city of Hama, a flashpoint for protests against Assad's regime.

On September 6, Ford strongly criticised Assad's regime in a statement posted on Facebook, denouncing in particular justifications for the violent crackdown against demonstrators.

The French envoy, Eric Chevallier, said he was the target of a similar attack on Saturday, when a crowd hurled stones and eggs at him after he met Greek Orthodox Patriarch Ignace IV in Damascus.

"The Shabiha (a pro-regime militia), some of whom had metal bars in their hands, and women threw eggs and stones in my direction and in the direction of my team, and looked threateningly at us while we were returning to our two cars," Chevallier told AFP.

Since mid-March, Syria has been shaken by an unprecedented pro-democracy protest movement that the Assad regime has sought to crush using deadly force.

More than 2,700 people have been killed in the unrest, according to the United Nations.